Conjugated diene rubber (e.g. a styrene-butadiene copolymer) produced by means of an emulsion polymerization method has been known as rubber used for automobile tires. In recent times, there are expectations for on improvements in low fuel consumption performance of automobiles, various types of conjugated diene rubber capable of ensuring excellent low fuel consumption performance have been proposed.
As an example, there is a proposal of a conjugated diolefin a (co)polymer rubber (in Patent Document 1) which has features of (1) being a (co)polymer rubber of conjugated diolefin(s) or a copolymer rubber of a conjugated diolefin and an aromatic vinyl compound; (2) having primary amino groups and alkoxysilyl groups binding to a (co)polymeric chain; and features that (3) monomers having bifunctionality or more are copolymerized in a (co)polymeric chain and/or a coupling agent having bifunctionality or more is coupled to at least part of a (co)polymeric chain.
As another example of such rubber, there is a proposal of modified diene polymer rubber (in Patent Document 2) which is obtained through a process step 1 of producing an active polymer with an alkali metal terminal by polymerization of a conjugated diene monomer or a conjugated diene monomer with an aromatic vinyl monomer in a hydrocarbon solvent in the presence of an alkali metal catalyst and a process step 2 of producing modified polymer rubber by allowing the active polymer to react with a compound represented by a specific formula.
Additionally, as a method of producing a modified polymer capable of promoting interactions with silica and carbon black and improving fracture characteristics, abrasion resistance and low exothermic properties, there is a proposal of a method (Patent Document 3) in which a primary modification reaction is performed by allowing a polymer having organometallic active sites in its molecule to react with a hydrocarbyloxysilane compound at the active sites, and then a secondary modification reaction is performed by subjecting the hydrocarbyloxysilane compound to reaction via condensation reaction between hydrocarbyloxysilyl groups.